Solved from its service manualAll synths

Four-Voice Netlist Synthesizer

APH-21Quadrifier

Four voices, screaming into the void, forever.

Four voices of a 1978 Japanese semi-modular, solved from its service manual part by part. Then two circuits it never had: a wave wrapper before the filters, and a folder that folds nothing but the resonance.

Hear it Tour the panel

VST®3 instrument · Windows 64-bit No activationmacOS VST3 and Audio Unit are in development.

The APH-21 Quadrifier panel in blackened steel with EXAMPLE pressed. Across the top, the APH-21 badge and QUADRIFIER, FOUR-VOICE SYNTHESIZER, the four VOICES lamps, the BOUNCE field reading 3 NETLIST over LIVE, MIXED ON BOUNCE, and PAN 1 to PAN 4. Below, VCO 1, VCO 2, PITCH MOD and TUNE, the MIXER and the WAVE WRAPPER; then the HPF, the LPF, the RESONANCE FOLDER with its RES lamp lit, and VCA and OUT; along the foot ENV 1 and ENV 2, each drawn as set, the LFO, the SIDE-CHAIN FOLLOWER and CONTROLS with WHEEL and PUSH. Down the right side the MODULATION MATRIX, three of its sixteen slots routed: WHITE to S&H IN, S&H to LPF CUTOFF, and ENV 2 to WRAP SHIFT.

4 voices
2 new circuits
24 sources, 26 destinations
8 bounce blocks

Four voices of a 1978 Japanese semi-modular, solved part by part from its service manual. Then two circuits it never had.

THE CLONE

Every voice is the whole voice circuit, oscillators to VCA, with one board of shared modules beside the four. Turn the new controls down and each voice is the stock circuit.

THE NEW CIRCUITS

A WAVE WRAPPER before the filters, and a RESONANCE FOLDER that folds the low-pass's ring and nothing else. Both are in the netlist, solved with the rest of the voice.

THE BOUNCE

Play it through a live model of the same voice. When your DAW renders, it solves the circuit, block by block, as much of it as you choose.

Listen

Six takes. Bounced through the netlist.

Six takes from the Quadrifier, thirty-two seconds each, in stereo. They are here as they were given, at the levels they came at, so the last one plays quieter than the rest.

TAKE 10:00 / 0:32
TAKE 20:00 / 0:32
TAKE 30:00 / 0:32
TAKE 40:00 / 0:32
TAKE 50:00 / 0:32
TAKE 60:00 / 0:32

The Quadrifier panel with EXAMPLE pressed, which the camera moves across module by module.

THE PANEL

Four voices, one panel.

Fifteen modules in blackened steel: the voice's path across the top two rows, the envelopes and the shared modules along the foot, and the matrix down the right side.

Then we made it gnarly

Two circuits it never had.

Both are built into the voice and solved with it, not effects after it: the wrapper feeds the filters, and the folder lives on the low-pass's resonance. Turn both down and each voice is the stock circuit again.

NEW · BETWEEN THE MIXER AND THE FILTERS

WAVE WRAPPER

A wavefolder turns a wave back at its limit. A wrapper carries it over to the other side: six transistor pairs step it back into a 5 V window every time it would leave, so a wave driven past the window comes out in pieces. DRIVE pushes the mix into it from one to six times, SHIFT moves the window off centre, SHIFT LFO lets the LFO move it, and MIX sets how much of the wrapped wave the filters hear.

NEW · ON THE LOW-PASS'S RESONANCE

RESONANCE FOLDER

It folds the resonance and nothing else. A twin of the low-pass runs beside it with no resonance; the difference between the two is the ring alone, with no bass in it, and that is what goes through the six folding pairs. FOLD drives it, BIAS makes the folds lopsided, and FOLD MIX blends it in. PARALLEL puts the folded ring back on top of the clean twin. IN-LOOP feeds it back into the filter as its resonance, and the filter screams through the folds.

2590

spectral lines in the low-pass's ring, PARALLEL

1088

spectral lines, IN-LOOP

Counted in SPICE on the netlist, before the fold and after it.

First, the clone

From the service manual.

Every voice is the original's voice circuit, read part by part from its service manual and written out as a netlist, and one more board of it holds the shared modules. In SPICE, the netlist's oscillators track within 0.6 percent across four octaves. Then the plug-in solves the same netlist with a solver of its own, and here is that solver against SPICE, block by block.

THE PLUG-IN'S SOLVER AGAINST THE SAME NETLIST IN SPICE
BLOCK	THE PANEL	HERE	SPICE
LPF	CUTOFF centre, RESONANCE full	497.5 Hz	500 Hz	sings on its own
HPF	CUTOFF centre, RESONANCE full	496.9 Hz	500 Hz	sings on its own
LFO	RATE full, then half	19.14 Hz, 9.03 Hz	19.2 Hz, 9.0 Hz	the rate
LFO	the triangle and the pulse	5.53 V, 5.11 V	5.5 V, 5.1 V	peak to peak, and high
NOISE	white, after six seconds	4.59 V	4.7 V	peak to peak

The 500 Hz is where the service manual's own adjustment procedure trims the filters, and each voice's oscillators are trimmed to their own circuit the same way.

The side-chain

Any track can play it.

Route a drum loop, a vocal or a guitar into the side-chain input, and the SIDE-CHAIN FOLLOWER turns it into control: its envelope, a gate whenever it passes THRESH, its pitch as a voltage, and its preamp and band-pass outputs. All five are sources in the matrix, so the track can open the filter, fold the resonance or fire the envelopes.

The MODULATION MATRIX with EXAMPLE pressed: slot 1 routes WHITE to S&H IN at +100%, slot 2 S&H to LPF CUTOFF at +50%, and slot 3 ENV 2 to WRAP SHIFT at -50%, its bar in blue. Slot 4's DESTINATION list is open in two columns, from PITCH to FOLLOWER IN, the last six in brass: LFO RATE, S&H IN, S&H CLOCK, AUX IN, AUX CV and FOLLOWER IN. Along the foot, EXAMPLE and CLEAR, and the note: routes add to the wiring; brass destinations are shared; a voice's source sends the average.

The patch bay's place

Sixteen routes. Nothing unplugged.

Sixteen slots, each a SOURCE, a DESTINATION and an AMOUNT either way: 24 sources, 26 destinations. The original's own wiring stays exactly where it was, VCO 2 into the FM, the LFO into the pitch and the filters, ENV 2 into both cutoffs, and every route adds to it. So no route can unplug the keys. EXAMPLE sets three routes and the knobs they need, and CLEAR empties the slots.

SOURCES

KEY
VELOCITY
GATE
ENV 1
ENV 2
VCO 1
VCO 2
RES
FOLD
VOICE OUT
LFO TRI
LFO PULSE
WHITE
PINK
S&H
AUX VCA
WHEEL
BUTTON
MOD WHEEL
FOLLOWER ENV
FOLLOWER GATE
FOLLOWER PITCH
FOLLOWER PREAMP
FOLLOWER BANDPASS

DESTINATIONS (brass: shared) (amber: new)

PITCH
VCO 2 PITCH
LIN FM
PW
VCO 1 LEVEL
VCO 2 LEVEL
MIX IN
WRAP DRIVE
WRAP SHIFT
WRAP MIX
HPF CUTOFF
HPF RES
LPF CUTOFF
LPF RES
FOLD
FOLD BIAS
FOLD MIX
VCA GAIN
ENV 1+2 TRIG
ENV 1 TRIG
LFO RATE
S&H IN
S&H CLOCK
AUX IN
AUX CV
FOLLOWER IN

The six brass destinations are on the shared board, so a voice's source sent there arrives as the four voices' average. A route to a knob turns the knob's own part in the circuit.

Playback and bounce

Play it live. Bounce it block by block.

Four solved circuits cannot keep up with your hands, so the Quadrifier plays a live model of the same voice, each stage's law worked from the netlist's own parts. When your DAW renders offline, with ENGINE on CIRCUIT, it solves the netlist for the blocks you choose and the live model plays the rest.

The BOUNCE menu open over the Quadrifier panel, headed WHAT AN OFFLINE RENDER SOLVES, BLOCK BY BLOCK: eight rows, OSCILLATORS, WAVE WRAPPER, FILTERS, RESONANCE FOLDER, VCA, ENV 1, ENV 2 and SHARED MODULES in brass, each with what it holds and a LIVE or NETLIST pair. WAVE WRAPPER, FILTERS and RESONANCE FOLDER are lit on NETLIST, the rest on LIVE, and under them ALL LIVE, DEFAULT and ALL NETLIST. Above it, the BOUNCE field reads 3 NETLIST.

OSCILLATORSVCO 1, VCO 2, pitch mod, portamento, the mixerLIVE
WAVE WRAPPERNEWthe six pairs and their summersNETLIST
FILTERSHPF, LPF, their cutoff summers, and the low-pass's twinNETLIST
RESONANCE FOLDERNEWthe ring, and the six fold cellsNETLIST
VCAthe VCA and INITIAL GAINLIVE
ENV 1delay, attack, releaseLIVE
ENV 2hold, attack, decay, sustain, releaseLIVE
SHARED MODULESLFO, noise, S&H, aux VCA, the followerLIVE
DEFAULT: 3 NETLIST, THE REST LIVE

THE DEFAULT

The three that matter most.

The wrapper, the filters and the folder are solved; the oscillators, the envelopes, the VCA and the shared modules are live. The filters and the low-pass's twin are one block, because the folder's ring is the difference between the two and only cancels when both come from the same engine.

WHAT IT COSTS

Slower than the song.

On our bench, over a four-second phrase with its warm-up, the default blocks took from about 4 times to about 21 times as long as the audio, the plainest patch to one full of noise. Every block solved took about 65 times as long. ALL LIVE renders faster than the song.

HOW CLOSE

The live model is a model.

On the default patch the live engine sits 0.38 dB from the whole netlist, and its third-octave bands 1.74 dB from it on average. Its VCA is the simplest part of it, so on loud patches set VCA to NETLIST and hear the circuit's own. If the circuit ever faults, the panel says so, the fault is logged, and the live voices carry on.

Every control

Blackened steel, in plain words.

The panel is 1600 by 900, and it uses the words any synth player already knows: LFO, ENV 1, RESONANCE, KEY TRACK. The voice modes, the unison detune, the bend range and the sustain pedal are in your host's parameter list, and four voices can play as POLY, UNISON or MONO, with LEGATO.

VCO 1

OCTAVE, 32' to 4'; WAVE, TRI, SAW, PLS or NSE; PULSE WIDTH and PW MOD; FM INDEX, and the LIN FM or EXP FM switch.

VCO 2

OCTAVE, 16' to 2'; WAVE, SAW, SQR, PLS or RING; and its own PITCH.

PITCH MOD · TUNE

How far the LFO and ENV 1 move both oscillators, PORTAMENTO, and MASTER TUNE.

MIXER

VCO 1 and VCO 2, each its own level.

WAVE WRAPPERNEW

DRIVE, SHIFT and MIX, and SHIFT LFO, how far the LFO moves the window.

HPF

CUTOFF and RESONANCE, LFO and ENV 2, DRIVE into it, and KEY TRACK.

LPF

CUTOFF and RESONANCE, LFO and ENV 2, and KEY TRACK.

RESONANCE FOLDERNEW

FOLD, FOLD MIX and BIAS, BIAS LFO, PARALLEL or IN-LOOP, and the RES lamp.

VCA · OUT

INITIAL GAIN, to hold the VCA open, and VOLUME.

ENV 1 · ENV 2

DELAY, ATTACK and RELEASE; HOLD, ATTACK, DECAY, SUSTAIN and RELEASE, each drawn as you set it.

LFO

SHAPE, from a rising ramp through a triangle to a falling one, RATE, and a lamp that blinks at it.

SIDE-CHAIN FOLLOWER

LEVEL, LOW CUT and HIGH CUT, PITCH CV and THRESH, with PEAK and GATE lamps.

CONTROLS

WHEEL and PUSH, a wheel and a button, both of them sources in the matrix.

VOICES · BOUNCE · PAN

Along the top: a lamp for each voice, the BOUNCE field and its menu, and PAN 1 to PAN 4.

What it is, and what it is not

Solved, read, and not yet.

SOLVED

Every voice's circuit and the shared board, with the wrapper and the folder in the same netlist, on the blocks the BOUNCE menu names. The power supply is left out, its rails ideal, and so are the lamps and the headphone amplifier. The keyboard is your host's.

READ, AND ESTIMATED

The manual draws the filter chip as a sealed box, so its insides come from published descriptions of it. Where a value on the page was unclear we read it and wrote the reading down. The transistors and diodes use close stand-in models of parts of their class, not measurements of the originals, the op-amps are behavioural models, and the live model is a model.

NOT YET

The Mac: it is Windows only for now, with the Mac VST3 and Audio Unit in development. Nothing on this page is for sale yet.

APH-21

Quadrifier

Four voices, screaming into the void, forever.

Hear it All synths

VST®3 instrument · Windows 64-bit No activationmacOS VST3 and Audio Unit are in development.

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